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تسجيل مستخدم جديدCosmological Constant in SUGRA Models Inspired by Degenerate Vacua
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It is well known that global symmetries protect local supersymmetry and a zero value for the cosmological constant in no--scale supergravity. A particular breakdown of these symmetries, which ensures the vanishing of the vacuum energy density, leads to the natural realisation of the multiple point principle (MPP). In the MPP inspired SUGRA models the cosmological constant is naturally tiny.
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We argue that the exact degeneracy of vacua in N=1 supergravity can shed light on the smallness of the cosmological constant. The presence of such vacua, which are degenerate to very high accuracy, may also result in small values of the quartic Higgs
coupling and its beta function at the Planck scale in the phase in which we live.
In N=1 supergravity the tree-level scalar potential of the hidden sector may have a minimum with broken local supersymmetry (SUSY) as well as a supersymmetric Minkowski vacuum. These vacua can be degenerate, allowing for a consistent implementation o
f the multiple point principle. The first minimum where SUSY is broken can be identified with the physical phase in which we live. In the second supersymmetric phase, in flat Minkowski space, SUSY may be broken dynamically either in the observable or in the hidden sectors inducing a tiny vacuum energy density. We argue that the exact degeneracy of these phases may shed light on the smallness of the cosmological constant. Other possible phenomenological implications are also discussed. In particular, we point out that the presence of such degenerate vacua may lead to small values of the quartic Higgs coupling and its beta function at the Planck scale in the physical phase.
It is well known that global symmetries protect local supersymmetry and a zero value for the cosmological constant in no--scale supergravity. The breakdown of these symmetries, which ensure the vanishing of the vacuum energy density, results in a set
of degenerate vacua with broken and unbroken supersymmetry leading to the natural realisation of the multiple point principle (MPP). Assuming the degeneracy of vacua with broken and unbroken SUSY in the hidden sector we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced in the split-SUSY scenario if the SUSY breaking scale is of the order of 10^{10} GeV.
In N=1 supergravity the scalar potential may have supersymmetric (SUSY) and non-supersymmetric Minkowski vacua (associated with supersymmetric and physical phases) with vanishing energy density. In the supersymmetric Minkowski (second) phase some bre
akdown of SUSY may be induced by non-perturbative effects in the observable sector that give rise to a tiny positive vacuum energy density. Postulating the exact degeneracy of the physical and second vacua as well as assuming that at high energies the couplings in both phases are almost identical, one can estimate the dark energy density in these vacua. It is mostly determined by the SUSY breaking scale M_S in the physical phase. Exploring the two-loop renormalization group (RG) flow of couplings in these vacua we find that the measured value of the cosmological constant can be reproduced if M_S varies from 20 TeV to 400 TeV. We also argue that this prediction for the SUSY breaking scale is consistent with the upper bound on M_S in the higgsino dark matter scenario.
In no--scale supergravity global symmetries protect local supersymmetry and a zero value for the cosmological constant. We consider the breakdown of these symmetries and present a minimal SUGRA model motivated by the multiple point principle, in whic
h the total vacuum energy density is naturally tiny. In order to reproduce the observed value of the cosmological constant and preserve gauge coupling unification, an additional pair of $5+bar{5}$--plets of superfields has to be included in the particle content of the considered model. These extra fields have masses of the order of the supersymmetry breaking scale; so they can be detected at future colliders. We also discuss the supersymmetry breakdown and possible solution of the cosmological constant problem by MPP in models with an enlarged gauge symmetry.
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